■J iXTitoun'-i'iiix. 



" petrifactions," we have mineral liutlies wUicli uwe tlieir existence 

 and characters to Hving beings wliich existed at foi-nier periods in the 

 liistory of tiie earth. For tliis reason, fossils, thongh composed of 

 mineral matter, cannnt 1)2 said ])ro])erly to belong to the mineral 

 kingdom. 



On the other hand, the objects which belong to the animal and 

 vegetable kingdoms differ from those which are compi'ised in the 

 mineral kingdom in the following jioints : a. They are composed of 

 few chemical elements, of which carbon, hydrogen, oxygen, and 

 nitrogen are the most important ; and these elements are combined 

 to form complex organic compounds, which always contain a large 

 ]iroportion of water, are very unstable, and are prone to spontaneous 

 decom]iosition. h. They are composed of diverse or heterogeneous 

 parts, M'hich have usually more or less definite relations to one an- 

 other. These heterogeneous but related parts are termed "organs," 

 and the objects jjosscssing them are said to be "organised." Some 

 of the lowest forms of animals have bodies composed of so uniform a 

 sulistance tli:it the}^ cannot be said to lie organised, as they exhibit 

 no definite organs. This exception, however, does not affect the 

 general value of this distinction, c. The}' are always nuire or less 

 definite in shape, ])resenting concave and convex surfaces, and being 

 bounded by curved lines, d. When they increase in size, or " grow," 

 they do so, not liy the addition of pai'ticles from the outside, but by 

 the rece]ition of foreign matter into their interior and its assimila- 

 tion there (technically called " intiissvi.sception "). e. Lastly, they 

 invariably pass through certain ])eriodic changes in a definite and 

 iliscoverable order, — these changes constituting life. 



All the objects, then, which fulfil these condition.s, are .said to be 

 alive ; and they all belong either to the aiiimal or to the vegetable 

 kingdom. The study of living objects of all kinds, irrespective of 

 whicli kingdom they belong to, is conveniently called by the general 

 name of BioJorfii ((Jr. /</o.s-, life ; and J<'<jm, discourse). As all living 

 objects, however, may be referreil to one or other (jf these two king- 

 doms, .so Biology may be divided into the two sciences of Butani/, 

 which treats of jilants, and Zoologi/ ((Ir. -r«V«, animal ; hnjos, dis- 

 C(jiusc), which treats of animals. The term Natural History, again, 

 is generally understo<jd nowadays as being ecjuivalent to Zoology 

 alone, though origijially it was appliwl to the study nf all natural 

 objects indi.scriminatcly. 



2. Differences between Anim.vls and Pl.\nts. 



It now becomes neces.sary to ini|uirc iiitii the diH'i-rcnces which 

 sulisist between animals and plants, .-uid which en.able us tii se|iar.-ite 



